1. Field of the Invention
The present invention relates to a method and apparatus for treating the surface of a body of natural rock or artificial stone-like material, to give to the latter surface an attractive finish. The method and apparatus use for that purpose a high temperature jet of plasma and a high speed jet of cooling fluid.
2. Brief Description of the Prior Art
A method which is presently widely used to treat surfaces of natural rocks, in particular granite, consists in heating the surface of granite to cause bursting of the crystals at the said surface to give to the latter a glossy and attractive finish. Actually, exploitation on an industrial scale of the above method makes use of a flame obtained through combustion of natural gas or other combustible fuel to heat the granite surface in order to carry out the desired treatment. U.S. Pat. No. 2,655,909 (R. B. Aitchison et al.) issued on Oct. 20, 1953, and U.S. Pat. No. 3,251,394 (M. L. Thorpe et al.) issued on May 17, 1986, both describe a treatment method of this type. Such a method is not only expensive, but is also slow whereby a treated slab of granite is heated throughout its thickness. Important stresses are thereby imposed to the granite material, which stresses frequently cause fissuring and cracking of the processed slab. This drawback considerably increases the minimum thickness of slabs of which the surface can be treated without risk of deep fissuring, breaking or the like.
U.S. Pat. No. 2,781,754 (R. B. Aitchison et al.) issued on Feb. 19, 1957, relates to the thermal texturing of a surface of natural rocks by means of a flame produced through an oxy-fuel gas blowpipe. The slab of rock is immersed in water to minimize heating thereof. This texturing method is also restricted to thick slab of rock, the minimum thickness being of about 1.91 cm (3/4").
U.S. Pat. No. 3,704,914 granted to Ralph Andrew Fletcher Jr. on Dec. 5, 1972 describes a method of cutting rock by means of a flame. The flame impinges upon a surface to be cut and material at the surface is rapidly heated by the flame to a state of massive incandescence. As heat penetrates and the heat front advances, there is also produced beneath the zone of incandescence a substrate of thermally fractured material. A jet of water is applied to the incandesced surface at an angle enabling it to penetrate the thermally fractured substrate. Obviously, the method of Fletcher Jr. heats deeply the rock material to result in the above discussed drawback.
French patent No. 2,251,178 granted to Humphreys Corporation and published on Jun. 6, 1975, proposes a method for producing deep grooves in a body of rock. The rock is dielectrically heated by means of an arc transferred between a jet of plasma and an auxiliary electrode, made of graphite, or between two jets of plasma. The method disclosed in French patent No. 2,251,179, capable of cutting deep grooves in a body of rock, is obviously not adapted to treat the surface of a thin slab of natural rock or artificial stone-like material.